The present invention relates to a fuel injection pump for an internal combustion engine. U.S. Pat. No. 3,006,556 discloses an injection pump comprising a locking mechanism which holds a drive rod for a pump piston on the injection pump and prevents it from being lost when the injection pump is separated from a mechanical drive element such as a driving cam, for example, during servicing. This arrangement also prevents a restoring spring which also acts on the pump piston via the drive route from accidently pulling the piston out of its cylinder. This safety mechanism comprises a bolt with a molded locking lug within a bore extending transversely through the drive route. The locking lug engages in a slot-shaped recess which is located in a rod guide tube embracing the drive rod. The spring which is also disposed in the bore extending at right angles to the drive route keeps the locking lug in the slot-shaped recess. Both the bolt and the spring are prevented from being accidently released from the bore by means of a locking ring or locking disc. By reason of the fact that this safety mechanism consists of a number of parts it is costly to produce and difficult to assemble. Furthermore, the flat-shaped recess prevents the drive rod from rotating freely because it runs essentially parallel to the longitudinal access of the drive rod.
U.S. Pat. No. 2,819,657 discloses an injection pump in which a locking bolt is inserted in a recess bored transversely in a stationary guide tube and penetrates a slot extending in the longitudinal direction of a coupling sleeve surrounding the drive rod. The bolt has a complicated shape and is therefore costly and during assembly its pin-shaped end must be inserted first into the opening. This safety mechanism also prevents free rotation of the drive rod.